Process for high-pressure spray extraction of liquids

ABSTRACT

A liquid high pressure splaying extraction process by means of compressed gas is disclosed. A liquid and gas are mixed in a mixing zone and substances contained in the spray particles that leave the mixing zone are separated in a separate loading zone, where spray particles are able to dwell for a sufficient period of time. Geometrically optimized flight paths for substance transfer are provided.

REFERENCE TO RELATED APPLICATIONS

This application is a 371 of PCT/EP95/03950 filed Oct. 6, 1995.

The invention relates to a process for high-pressure spray extraction ofliquid solutions and suspensions in the pressure range up to 1,000 barby means of compressed gases such as CO₂, propane, butane and mixturesthereof with and without entrainer additives such as: ethanol, propanol,methanol, acetone, water, methyl-ethyl-ketone, comprising liquid and gasmixing and mass transfer.

As is well known, the setting of an optimal dwell time is necessary forextraction processes. In discontinuous batch processes, this is producedby the period of extraction gas impact (DE 33 16 705 A1). As opposed tothis, the process according to the invention allows the continuousguiding of the extraction gas while at the same time ensuring optimaldwell times for the liquid in this gas.

The use of alternating pressure impact for reducing the size of solidsis known (DE 26 32 045 C2). With extraction procedures with compressedgases, however, the dispersion of a liquid must take place with aslittle pressure loss as possible because otherwise, the solubility ofthe gas decreases considerably and extraction becomes impossible. Analternating pressure impact would also be disadvantageous because theattainable drop ranges would then no longer be constant in time andproduct quality would thus be nonuniform. The technical problem of theinvention is therefore to indicate a high-pressure spray extractionprocess in which a constant fine-dispersion of the liquid is achieved ina spraying device without alternating pressure impact and the optimaldwell time is set in an appropriate extraction geometry.

Unlike known nozzle extraction processes, in high-pressure sprayextraction the charging does not take place in a mixing chamber, rathera distinction is made between a mixing zone and a charging zoneadjoining it.

The spatial separation of the two process steps "mixing" and "charging"is advantageous physically speaking, because with a variable design ofthese two zones according to the invention

a) during mixing, a substantially increased turbulence or finer dropformation can be set compared to known devices

and

b) in the subsequent charging zone, the spray particles emerging fromthe mixing zone can be given an adequate dwell time and geometricallyoptimized flight trajectories for the mass transfer (charging).

Compared to conventional spraying processes, high-pressure sprayextraction offers the advantage that the prevailing process conditionshave a positive effect on the spraying. The solubility of the gas in theliquid, substantially increased under pressure, leads to a considerablereduction in viscosity, in such a way that the liquid can be more easilydispersed into drops. But particularly the reduction of the interfacialtension between the phases to be mixed, noted as pressure increases,causes small drops to form (documentation: computer-assistedphotographic image of two drops in supercritical carbon dioxide underdifferent levels of pressure).

Furthermore, the mixing zone should be geometrically designed in such away that due to an optimal pulse exchange, the high kinetic energy ofthe compressed gas is utilized to disperse the liquid into small drops.The spatial layout of the mixing zone for the spray extraction can beimplemented as a two-substance nozzle with high-turbulent cross-flow orswirling flow of the gas as well as two single-substance nozzles (impacteffect) directed toward each other. The use of a static mixer withsubsequent unitary atomization of the gas and liquid is alsoconceivable.

The design of the charging zone is determined by the dwell timenecessary for the mass transfer. A cylindrical design is sensible forrelatively brief dwell times, e.g. for removing the oil from crudelecithin, because the mass transfer is completed before the sprayedparticles hit the wall of the charging zone. There are greater transferresistances for aqueous phases, such that the charging zone must allowlonger dwell times without wall contact, e.g. a spherical or cut-offcone shape is advantageous for the separation of caffeine or nicotinefrom aqueous solutions. The same is true when the absorbing phase mustbe charged with nearly the entire feed stream, e.g. with crude oildesliming, in which approx. 98% of the feed stream goes into solutionand the phosphatides are separated in the charging zone.

Along with the extraction, a certain particle formation can also bestrived for. For this, it is sensible to present a different gas in theextraction zone than the one used for the extraction. The gas mixtureforming is then marked by a modified solution quality, in such a waythat the desired substances turn out as microcrystalline particles(example: extraction with CO₂ in an extraction zone with N₂).

Application of the process according to the invention

The high-pressure spray extraction with separate mixing and chargingzone is suitable for genuine separation problems such as:

removing the oil from crude lecithin

desliming of crude oil

removing the oil from hydrolyzed soybean lecithin

removing the fat and removing the cholesterol from liquid eggs

lipid extraction from biomasses from fermentation

extraction of distilled oils and aromas from aqueous or alcoholic plantextracts

removal of active ingredients from aqueous solutions

caffeine from coffee or tea extracts, ginseng, pesticide removal fromaqueous or oily plant extracts (e.g. hop)

extraction of microcrystalline substances, e.g. medicines for inhalers)from solutions, whereby the solvent is soluble in compressed gas(mixture) (e.g. ethanol, water, among other things)

drying of aqueous solvent-containing mixtures.

It is also suitable for the production of new products, e.g. for coatingantibiotics with phospholipids that were dissolved together beforehand,e.g. in an alcohol mixture that changes into supercritical gas in thecharging zone. Thus, applications for high-pressure spray extractionopen up in the domain of pharmaceutical and dietetic products.

BRIEF DESCRIPTION OF THE DRAWINGS

The invention is described in what follows with reference to thedrawings.

FIG. 1 shows a flow chart of the system for executing the processaccording to the invention.

FIGS. 2-4 show schematic embodiments of the mixing zone.

FIGS. 5-7 show schematic embodiments of the charging zone.

FIG. 8 shows a charging profile for the fluid in a tubular chargingzone.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

Removing the oil from lecithin

Crude soybean lecithin is mixed in a process according to FIG. 1 asmedium in the inner mixing chamber of a two-substance nozzle with asupercritical fluid under extraction conditions in the cross-flow and isthen sprayed as drop dispersion into a cylindrical charging zone (14.3mm inside diameter). In the two-phase flow, with dwell times of 20s to40s, the fluid phase absorbs so much oil from the crude lecithinparticles that they are almost completely oilfree. The deoiled lecithinis separated mechanically (cyclone) from the fluid stream and becomesavailable as valuable substance in powder form in the raffinatecollector, while the charged fluid is regenerated in an extractseparation stage at reduced pressure levels and temperatures. Bycompression in a pump and temperature setting in a heat exchanger, theregenerated fluid can be fed again to the mixing zone in the circuit.

When using carbon dioxide as fluid phase, the following processparameters are set:

Extraction pressure: 350 bar-1000 bar (preferably: 450 bar-700 bar)

Extraction temperature: 60° C.-150° C. (preferably: 100° C.-140° C.)

Mass flow ratio

(kg fluid/kg medium): 25-100 (preferably 50-75)

Separating pressure: 50 bar-200 bar (preferably: 100 bar-150 bar)

Separating temperature: 20° C.-80° C. (preferably: 40° C.-60° C.).

A crude soybean lecithin with an approx. 65% phosphatide content can bedeoiled to a residual oil content of less than 1.5 percent by weightunder the preferred conditions.

Very high turbulence is achieved in the mixing zone with Reynoldsnumbers of 100,000-200,000. A turbulent two-phase flow is preferablyalso set in the adjacent charging zone with Reynolds numbers of30,000-50,000.

Crude oil desliming

Crude oil desliming, in which the raffinate resulting from the chargedfluid phase as well as the extracted oil form the valuable substances,is carried out under the same extraction and separation conditions asthe removal of oil from lecithin. Due to the high 98% oil portion goinginto the fluid phase, the mass flow ratio must accordingly be raised to100-300. Although the charging should preferably be carried out in aspherical geometry, a desliming to a phosphorus content of 78 ppm in theoil could already be achieved in a tubular charging zone at 700 bar and120° C.

Continuous system operation

Until now, no possibility was known to continuously extract from anautoclave a powdered solid as results as raffinate from lecithindeoiling.

Tests have shown that compressed lecithin forms a pressure sealed plug.In this way, an extraction via a pressure-proof extruder with subsequentgas-blocking segment is possible. The lecithin compressed in theextruder forms a pressure-sealed plug in the gas-blocking segment and isextracted as such. This is conceivable particularly when using aself-cleaning twin-shaft extruder, because the transfer is brought to astandstill in a single-shaft extruder due to the cohesion at the screwwalls.

For a quasi-continuous operation, the use of two or more extractorsoperated alternating in batch process and consisting of the atomizingdevice, the extraction zone and the collector has proven effective.During the emptying of a raffinate collector, the extraction can becontinued in another extractor.

Separation of the solid matter transferred

Solid particles are also carried along with the charged oil in the flowfrom the raffinate collector into the oil separator. This loss ofproduct is attributable to the inadequate separation under gravity dueto the small difference in density between the solid matter and thecompressed gas. Adequate solid matter retention in the raffinatecollector is attainable only in the tangential field. For this, atangential intake of the two-phase flow is provided in the raffinatecollector and, in addition, a high-pressure cyclone is installeddownstream under extraction conditions. Only after the high-pressurecyclone is the pressure for the oil separation reduced.

Extraction and separation conditions

The pressures and temperatures in the extraction and separation areashould be matched in such a way that energy-saving operation withfavorable extraction results can be achieved. In this connection,extraction pressures of 480 bar have proven effective for removing theoil from crude lecithin. At temperatures of 120° C. to 140° C., thedensity of the extraction gas is lowered with increasing solubility forthe valuable substance to be absorbed, in such a way that charging aswell as solid matter retention according to 2.4 are effective.

On the other hand, oil separation is to be carried out at pressures ashigh as possible, so as to reduce the expenditure for recompression ofthe circuit gas. For this reason, separation conditions under which thegas remains supercritical are suitable. A separating pressure of 150 barhas proven effective at temperatures that set in after tension isreleased (50° C. to 70° C.). The recompression of the circuit gas cantake place under supercritical conditions in such a way that due to thecompression heat, the extraction temperature is attained. In this way,the cooling for liquefaction of the gas before recompression as well asthe heating after recompression can be saved.

Atomization of the material used

In a known process (EP 0 137 214), the material used is combined withthe extraction gas stream in a nozzle-like mixer. This mixer should bereplaced by a genuine atomization. The purpose of the atomization is togenerate small drops which are extracted in a separate extraction zonewith short diffusion paths.

For the materials used, there is the possibility of a viscosityreduction before atomization. For highly viscous natural substances(e.g. crude lecithin), this can be achieved by preheating to a maximumof 70° C. and premixing with a partial stream of extraction gas. Theviscosity can be reduced by 10 times by premixing. A continuouspremixing of the material used is achieved in a static mixer coveredwith a pressure tube.

Disintegration of the drops of a highly viscous liquid in the gas streamis achieved only inadequately by the guiding, proposed in theabove-mentioned patent, of the extraction gas "in the same direction" asthe mixture. For the technical execution, a nozzle form should be chosenin which the extraction gas stream shatters the material streamcrosswise to its entry. In this way, the flow pulse of the extractiongas can be used completely for forming drops. The two-phase mixture isformed in an inner mixing chamber of the nozzle before it is sprayedthrough a taper into the extraction zone.

In addition to such a cross-flow nozzle, a swirling nozzle is alsoconceivable, in which the gas stream is guided in a swirling flow. Aswirling flow cannot be impressed on a highly viscous material, so thematerial enters the swirling stream of the extraction medium crosswiseto it, is reduced in size in so doing, and the drops formed are carriedalong in the swirling stream as a mixed flow. Then the spraying into theextraction zone also takes place.

Extraction zone

The extraction zone should be designed as an autonomous system componentdownstream from the atomization. The turbulence and the dwell time ofthe two-phase flow between the particles formed in the atomization andthe extraction gas are regulated in the extraction zone.

In principle, the extraction zone may be designed as a pipe section oras a container. The pipe section is suitable for media that develop apourable solid immediately after emerging from the atomization (e.g.lecithin). Media that form liquid drops (e.g. crude soybean oil) or forma solid only after an extraction period of finite length must be sprayedinto a container with larger diameter (ideal: spherical container),because these media would develop a liquid film on the wall of a pipesection and the surface enlargement obtained during atomization would beeliminated.

The two-phase flow from the extraction zone is guided directly into araffinate collector in which the raffinate can settle.

With reference to the drawings the following details are provided:

FIG. 2 shows an embodiment of the mixing zone as a two-substance nozzlewith cross-flow guiding and inner mixing chamber.

FIG. 3 shows the outer mixing in the impact stream of twosingle-substance nozzles that are being fed by the fluid and the mediumused.

FIG. 4 shows cross section views and longitudinal section views of thedevelopment of a swirling nozzle, and the fluid may essentially be fedtangentially and the medium used may essentially be fed axially.

In FIG. 7 the charging zone is shown as a blunt cone 7.

An illustration of the changing profile of the fluid in the tubularcharging zone is shown in FIG. 8, with the relative fluid charging beingshown along the length of the charging zone. The individual parametersare detailed in the illustration. The mixing zone is indicated as A andthe charging zone is indicated as B/C.

We claim:
 1. A process for high-pressure extraction of media from liquidsolutions and suspensions in the pressure range up to 1,000 bar by meansof compressed gases, involving liquid and gas mixing and mass transfer,comprising:mixing in a mixing zone a flow of a compressed gas with aflow of a liquid containing a medium to form a spray containing sprayparticles comprising the liquid, the medium and the gas; directing thespray particles from the mixing zone to a charging and extraction zonespatially separated from the mixing zone; providing an adequate dwelltime of the spray particles in the charging and extraction zone toenable mass transfer to occur; and geometrically optimizing flighttrajectories of the spray particles for the purpose of mass transfer inthe spray particles.
 2. The process of claim 1, wherein the steps ofproviding adequate dwell time and optimizing flight trajectoriescomprise, where the mass transfer of the media is complete immediatelyafter the mixing, providing the charging and extraction zone with afirst cross sectional area sufficient for complete mass transfer of thespray particles during flight and, where the mass transfer of the mediais complete only after an extraction period of finite length, providingthe mixing and extraction zone with a second cross sectional areasufficient for complete mass transfer of the spray particles duringflight, said second cross sectional area being larger than said firstcross sectional area.
 3. The process of claim 1, wherein the steps ofproviding adequate dwell time and optimizing flight trajectoriescomprise, where the mass transfer of the media is complete immediatelyafter the mixing, providing the charging and extraction zone with acylindrical shape for complete mass transfer of the spray particlesduring flight and, where the mass transfer of the media is complete onlyafter an extraction period of finite length, providing the charging andextraction zone with a shape in which the cross sectional area increaseswith increasing distance from the entry of the sprayed particles intothe charging and extraction zone for complete mass transfer of the sprayparticles during flight.
 4. The process of claim 3, wherein the steps ofproviding adequate dwell time and optimizing flight trajectoriescomprise providing the charging and extraction zone with one of aspherical shape and a frustoconical shape for media for which the masstransfer is complete only after an extraction period of finite length.5. The process of claim 1, wherein the compressed gases comprise amember selected from the group consisting of CO₂, propane, butane, andmixtures thereof.
 6. The process of claim 1, wherein entrainer additivesare added to the compressed gases.
 7. The process of claim 6, whereinthe entrainer additives comprise a member selected from the groupconsisting of ethanol, propanol, methanol, acetone, water, andmethyl-ethyl-ketone.